1. Field of the Invention
The present invention relates generally to the field of devices for preventing or detecting tampering with electric watthour meters and, in particular, to an electro-mechanical anti-tampering device which utilizes a sensitive normally-closed electrical switch to actuate a mechanical or other device to respond to several types of attempted tampering.
2. Description of the Prior Art
The use of induction type watthour meters installed in meter sockets at customers' sites is well known in the electric utility metering field. Total electrical energy consumption is indicated on one or more register dials on the watthour meter which are driven by a geared disk which, in turn, is driven by a shunt induction motor. This system continually increments the dial or dials to show total electrical energy use. The dial or dials are read periodically for the purposes of billing by utility companies. Thus, the dial on the electric watthour meter is normally the only check which the utility company has pertaining to the total electric energy consumption by a particular customer. This had led to wide-spread tampering of watthour meters in an effort to reduce the indicated consumption and thereby defraud the utility company through indication of less-than-actual power consumption. The Edison Electric Institute (EEI) estimates that the total United States utility industry loses more than four hundred million dollars annually to meter cheaters. Other estimates by utility experts run as high as two billion dollars annually.
A large share of the meter tampering is done by residential and commercial customers with single phase induction watthour meters. Of the more than twenty-five commonly detected methods of meter tampering, more than two-thirds of these require either removal of the meter from its socket or removal of the cover glass.
One well known method of meter tampering which involves removal of the meter from its socket and reinstallation of the meter in an upside down position so that the terminals are reversed and the meter registers are caused to run in reverse, thereby reducing the total indicated power consumption without interruption of the power supply to the user. Other popular methods include delivering a blow to the meter such that the induction drive system is permanently disturbed and the mechanism runs at a slower rate for a given amount of power throughput, and using an external magnet to slow or even stop the operation of the induction disk drive system. In some cases the glass is removed and the dial readings changed or the operation of the mechanism otherwise interfered with to affect the meter reading. In a publication entitled "Meter Tampering Report" published in June 1978 by Texas Electric Cooperatives, Inc. it is estimated that the above overt methods account for about 85% of the total meter tamperings. Other, more subtle, methods account for the remainder.
One clever prior art approach to the problem associated with reinserting the meter upside down is disclosed in U.S. Pat. No. 4,039,943 issued Aug. 2, 1977. If the meter is equipped with a gravity switch which together with an auxiliary magnet cooperates not only to cause the meter to operate in the forward direction when installed upside down, but also causes it to run at a greater rate than that indicated by the actual power consumed, thereby penalizing the defrauder.
Ball-type normally-closed switch devices have been used in the prior art to open shunt circuits and take electric meters completely out of service such as that shown in U.S. Pat. No. 846,624 issued Mar. 12, 1907 to W. L. Saunders. While tampering in the case of that meter may temporarily take the meter out of service, replacement of the meter will put it back into service without any further indication of tampering. There remains a need for a low-cost, sensitive device which can be retrofitted into existing meters and which will readily detect the most common types of meter tampering.
SUMMARY OF THE INVENTION
By means of the present invention, there is provided an electro-mechanical tamper indicating or warning device which will detect movement of the cover or meter, any excessive vibration or impact or the presence of an externally applied magnetic field. A metallic ball is mounted in a torroidal shaped run having at least one inner and a plurality of outer contacts such that the ball in any one of a multiplicity of stable positions around the center post bridges the center post contact and one of the contacts along the outer circumference of the torroidal switch. In this manner the switch is normally closed and any disturbance that causes motion of the ball will at least momentarily open the switch as the ball moves off of the particular outer contact against which it has come to rest. Thus, any disturbance of the meter which causes motion of the ball will open the switch. By making the ball of a magnetic material, the presence of a magnetic field also will cause the motion of the ball and trigger the switch opening.
The anti-tampering switch of the invention can be used to trigger a servo system which might include a microminiature piston actuator which may be activated by an explosive designed to deliver a linear force. The motion of the piston can be made irreversible and used to mark the tampering event by any desirable means such as a witness block. Of course, the opening of the switch may be utilized to trigger an alarm or any other device to instantaneously indicate tampering, however, the operation of the piston will provide a permanent record noticeable at the next meter reading.
The ball switch is normally mounted on the cover glass to provide better sensitivity to external events concerning the meter. The switch can be connected electrically in the manner necessary utilizing power supplied by conversion from the shunt circuit running through the watthour meter itself and thereby can be retrofitted to existing meters. Similarly, the device can also be interlocked with the cover plate of the meter socket to detect tampering activities with the socket rather than the meter itself.